On Northern Ireland, the picture is mixed. The gross security errors of Bloody Sunday, internment and the Falls Road curfew, crucial iconic incidents in poisoning the relationship between the British Army and many Catholics, all of which directly strengthened the Provisionals, all took place earlier in his term of office, and Heath must carry ultimate responsibility for all three (including internment, technically Faulkner's decision but one that could hardly have been taken without Heath's knowledge or consent). Suspending Stormont was obviously the right thing to do - but perhaps this should have happened much sooner. And Heath then further bolstered the legitimacy of the Republican movement by flying in Martin McGuinness and Gerry Adams (as spokesmen for the IRA, note, not Sinn Fein) for the famous London talks with Willie Whitelaw.
On the other hand, Sunningdale was indeed an accomplishment - an agreement in many ways less flawed than the 1998 one (voluntary coalition rather than forced, largely brokered by Heath himself, and essentially wrecked by Harold Wilson's failure to stand up to Loyalist intimidation. Some analysts blame Heath for calling the first 1974 election early, and handing the Loyalists the propaganda coup of winning 11 out of 12 Northern Ireland seats. I would defend him on this - the election was coming at some point anyway, and in those days Westminster elections were practically second-order elections in Northern Ireland. It should also be said that the whole Sunningdale process, from the suspension of Stormont in early 1972 to the inauguration of the power-sharing executive in 1974, took less time than even the 1996-98 Mitchell talks, let alone the entire process from Downing Street Declaration of December 1993 to the present day.
I don't write much here about Northern Irish politics, but two sites which I do scan from time to time are the Slugger O'Toole weblog, providing commentary from a number of different perspectives, and The Blanket, which also presents a diversity of views, but is essentially run by disgruntled Republicans who believe that Gerry Adams has essentially settled for the same deal that was on offer in 1974, and complain that this devalues the entire armed struggle since then. I'd put it a little differently; I agree that Gerry Adams has indeed essentially settled for the same deal that was on offer in 1974 (strictly, 1973), but would say this demonstrates the worthlessness of the entire armed struggle since then.
Going back to Heath, two last notes. First off, last night's TV documentary showed how important he was in getting the UK into the European Economic Community as then was (and didn't mention Northern Ireland once). This is probably his most valuable political legacy, and he deserves a great deal of credit for it. Second, a friend of mine stood against him in Old Bexley and Sidcup in his last election, in 1997. The national papers ran a feature on the largest age gap between any two candidates in the same constituency - 54 years: Heath was then 80, while Iain had been born in the week of decimalisation, when Heath had already been prime minister for six months. Heath won handsomely, of course, but for the last time.
[Edited to add] Journalistic assessment from Belfast Telegraph here. Key phrase, "the Sunningdale settlement turned out like so much of the Heath record, to be either a glorious failure or too much too soon".